1. Field of the Invention
The invention relates to an assembled battery in which a plurality of rechargeable unit cells are connected in series, a manufacturing method of this assembled battery, and a vehicle provided with this assembled battery.
2. Description of the Related Art
An assembled battery, which is formed by connecting a plurality of unit cells which may be lithium ion batteries (cells) (in this specification, the terms “battery” and “cell” have the same meaning and may be used interchangeably) which are light and are capable of obtaining high energy density, nickel-metal hydride batteries, other secondary batteries, or power storing elements such as capacitors, together in series, is a power source from which high output can be obtained. For this reason, assembled batteries are gaining importance as in-vehicle power sources or power sources for personal computers and portable terminals. Japanese Patent Application Publication No. 2001-57196 (JP-A-2001-57196), for example, describes one example of an in-vehicle assembled battery that is formed by arranging a plurality of individual nickel-metal hydride secondary batteries of the same shape and connecting a positive terminal and a negative terminal provided on each unit cell in series. Also, assembled batteries in which a plurality of lithium ion batteries, which are lightweight and can deliver high energy density, are connected together in series are preferable for use as in-vehicle high-output power sources.
However, it is given that assembled batteries which are mounted in a vehicle such as an automobile are subject to limitations with respect to mounting space and will be used in an environment where vibrations occur. Therefore, as described in JP-A-2001-57196, the assembled battery is constructed with multiple unit cells arranged and fastened together (i.e., each unit cell is fixed to another). When fastening the unit cells together, a substantial load is applied to the individual unit cells which together form the assembled battery. On the other hand, the assembled batteries themselves must be lightweight, particularly if they are to be used in vehicles. Therefore, it is desirable that the container main body of the unit cell (i.e., the outer case that houses the electrode body and the electrolyte) also be lightweight. For example, it is preferable to use a container made of thin metal or synthetic resin. However, a container made of such a thin material tends to deform under an external load. That is, when unit cells provided with such containers are used and a plurality of these unit cells are arranged and fastened together in the direction in which they are arranged (i.e., the arranging direction), the container main body of the unit cells tends to flex or deform in the direction in which the load is being applied. This deformation of the container main body causes deviation and variation in the distance between, and the relative positions of, the positive and negative electrode terminals to be connected in series provided on each unit cell with respect to the ideal values of the initial design. Such variation in the distance between, and the relative positions of, the positive and negative electrode terminals when the unit cells are fastened together may render the terminal connectors, which were manufactured to the shape and size corresponding to the ideal values, unusable for example. Thus, an increase in cost and a decrease in work efficiency related to the work of connecting the positive and negative electrode terminals may result. Moreover, deformation of the unit cell containers that occurs when the unit cells are fastened together may result in the containers and electrode bodies of the unit cells no longer being sealed (air-tight) (i.e., the seal (air-tightness) may be lost).